Turns out that most of the frame-rate bottleneck wasn't even anything graphics-related. It was checking for screen width and height on Android on every mesh draw which is much slower than checking GLSurfaceView dimensions for aspect ratio. Vertex lighting by expanding from room center until you hit walls works well, but produces glitches, especially where voxel chunks meet. The new higher frame-rate makes the fireballs fly faster, which makes the game harder. But it now runs smoothly even on my $100 ZTE phone.
What is next for Fateless? More weapons, more monsters, more levels.
First many congrats on getting it to work on my old Nexus 7 tablet at all.
It runs reasonable speed, maybe 20fps or so.
If I was to be critical I would say I found the left hand thumb, forward backward and strafe to be incredibly hard to control. I'd have preferred just having a forward and backward button it was that hard to use. Don't know whether it was because I wasn't used to it or it was some frame rate dependent thing. The right thumb was a little laggy too but not impossible to use.
This shouldn't ever happen, try and make all your critical gameplay independent of frame rate. You'll get wildly varying frame rates / variation on different devices.